1. Field of the Invention
The present invention relates generally to tape reels for tape drives, and more particularly to take-up or supply reels for controlled uniform stacking of storage tape in tape drives to reduce lateral tape motion.
2. Description of the Related Art
Magnetic tapes are commonly used for data storage in computer systems. Magnetic tapes are typically housed in open reels, tape cartridges, and tape cassettes. Open reels include a hub upon which the tape is wound and flanges that protect the tape edges but are not housed in a container. When open reels are used in a magnetic tape drive, the tape from one reel (a supply reel) is spooled onto another reel (a take-up reel). A tape cartridge typically includes a container having a single reel upon which the tape is initially wound. When a tape cartridge is used in a magnetic tape drive, the tape on the reel in the tape cartridge is spooled onto a take-up reel in the magnetic tape drive. A tape cassette typically includes a container having two tape reels, a supply reel upon which the tape is initially wound and a take-up reel. When a tape cassette is used in a magnetic tape drive, the tape on the supply reel in the tape cassette is spooled onto the take-up reel in the tape cassette. Thus, when a tape cassette is used, the tape stays within the cassette container.
As a tape moves between a supply reel and a take-up reel during operation, the tape is guided over a read/write head to read data from and/or write data to the tape. However, transverse motion of the tape relative to the read/write head (lateral tape motion) as the tape moves between the supply and take-up reel may cause misalignments between the recorded track positions on the tape and the head. Such tracking errors may reduce data reliability. For example, during a write operation, lateral tape motion may prevent straight tracks from being written on the tape and may result in subsequent read errors. During a read operation, lateral tape motion may prevent the read head from being aligned at the center of the desired track on the tape, which may lead to data errors.
Multiple parallel tracks are typically written on a tape to increase the data rate capability of the tape. In general, the greater the number of tracks positioned on a tape, the more information may be stored on the tape. Consequently, track separation on tapes has continued to decrease in order to accommodate more tracks and greater storage capacity. As a result, it is desirable to control lateral tape motion as the tape passes over a read/write head during read/write operations in order to ensure that the desired track is accurately positioned on the head for read/write operations.
One approach to reduce lateral tape motion has been to ensure that the tape is stacked uniformly on both supply and take-up reels. As shown in FIG. 1 (prior art), as each individual loop stacks, the tape may slide laterally up or down as it spools around the reel. As such, the tape is non-uniformly stacked on the reel. Non-uniform stacking of tape on the reels may cause the tape to experience lateral motion as it is unwound and passes over a read/write head.
When tape spools on a reel, it squeezes out the layer of air that is trapped between the outer surface of the tape in the reel and the in-coming tape. By increasing tape tension and surface roughness of the tape, the tape may be more uniformly stacked on the reel because the trapped layer of air is more efficiently removed. The use of higher tape tension to reduce the sliding up and down of the tape as it spools on the reel, however, is less effective when using thin tapes typically used in current tape drives. Additionally, high tape tension increases the read/write head and tape wear, which reduce the life of the tape.